Small, thin batteries, such as button-type batteries, are commonly used in modern devices. For instance, button-type batteries are utilized as power sources for calculators and watches.
A prior art button-type battery 10 is shown in FIG. 1. Battery 10 comprises a lower terminal housing member, or can 12, and an upper terminal housing member, or lid 14. Can 12 and lid 14 are sealingly joined together at a crimp 16. Battery 10 is typically in the shape of a circle, with crimp 16 extending entirely around a periphery of the circle. A gasket material 18 is provided within crimp 16 to form a fluid-tight seal within the crimp. A cathode 20 and an anode 22 are provided between terminal housing members 12 and 14. Cathode 20 has a thickness of greater than 13 mils, and is generally not durable unless it has a thickness of greater than 24 mils. Cathode 20 and anode 22 are separated by a porous separator 24. An electrolyte 26 is provided within the battery and within porous separator 24.
Battery cathode 20 typically comprises a mixture of an active material and a conductive medium, or diluent. The active material can be, for example at least one of manganese dioxide and (CF).sub.x. The manganese dioxide provides a source of oxidizing component in a battery cell. As manganese dioxide is itself a poor conductor, the conductive medium is added to provide electrical conductivity. The conductive medium can be, for example, elemental carbon. The elemental carbon is typically in the form of graphite, although other materials, such as, acetylene black can also be used. Natural graphites can be used in alkaline cells, but typically cells are made with very pure synthetic graphite to reduce impurities which might lead to corrosion in a battery cell.
A difficulty in forming battery cathodes occurs in binding a conductive medium with an active material. A goal is to develop binders which produce dense, stable cathodes having good electronic and ionic conductivity, and efficient discharge even at high discharge rates. Another goal is to develop binders which form cathodes which can be very thin, and yet durable enough to be utilized with pick and place automation. Also, a goal is to develop binders which are simple to incorporate into manufacturing processes by which battery cathodes are produced. It would be desirable to develop methods of forming battery cathodes which achieve one or more of the above-discussed goals.
There is a continuing goal in small battery fabrication to form the batteries increasingly thinner, while maintaining efficient power discharge and physical durability. Limitations in battery thickness are imposed by limitations of the thicknesses of battery components, such as the anode and the cathode. Accordingly, it would be desirable to develop methods for forming thinner battery components which have good physical durability and efficient power discharge.